The Acid Bile Sack is a component of Bob the Living Fortress, serving as a breaching tool. It can cause damage to surfaces, capable of creating deep grooves in a target's mass.
The Acid Bile Sack was noted during the assessment of narrow bridges that Bob the Living Fortress could not cross, indicating its utility in combat situations. During an encounter with a colossal guardian, the Acid Bile Sack was hurled by Bob the Living Fortress, successfully impacting the guardian and demonstrating its effectiveness as a weapon. The party recognized its potential to breach defenses and inflict harm on formidable foes.